1. Field of the Invention
This invention relates to a process for the reduction of zinc oxide to elemental zinc in a more economical manner.
2. Description of the Prior Art
Most zinc ores are sulfides (ZnS) that are first converted to oxides (ZnO) by roasting the sulfide in hot air. The resulting oxide is normally referred to as zinc roast. Various processes have been used for reducing zinc roast including a horizontal retort process, a continuous vertical process, an electro-thermic smelting process, and a blast furnace process. The horizontal retort process is a batch method requiring from 24 to 48 hours per batch. The continuous vertical process requires special preparation of the feed material in which zinc roast, carbon, and binder are pressed into briquets which are then dried and heated to coking temperatures. This process also requires external heating for which reason the rate of reduction is limited by heat transfer. The electro-thermic smelting process requires careful preparation of the feed material. Finally, the zinc blast furnace process requires shock cooling of the exit gas by passing it through an intense rain of molten lead, involving about 400 tons of lead per ton of zinc.
Another method for the extraction of zinc, such as disclosed in U.S. Pat. No. 3,271,134, involves the reduction of zinc oxide with finely divided carbonaceous material such as pulverized coke breeze or anthracite dust in a stream of oxygen containing gas. Among other things this process involves the danger of igniting the carbonaceous material and thereby overcoming the primary object of reducing zinc oxide.